Position sensor, method for detecting horizontal and vertical position, alignment apparatus including position sensor, and method for horizontal and vertical alignment

ABSTRACT

A position sensor has an interface structure between negative dielectrics and a dielectric, and is provided with a configuration in which the plasmon intensity with respect to a microstructure in a surface including the interface structure or in the vicinity thereof is detected by the interface structure, and the positional relationship between the interface structure and the microstructure is thereby detected.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a position sensor, a method fordetecting a position, an alignment apparatus including the positionsensor, and a method for alignment.

2. Description of the Related Art

Contact exposure apparatuses, in which a mask pattern is brought intointimate contact with a resist on a wafer and exposure and transfer areperformed, are previously known as exposure apparatuses for fabricatinghigh-density semiconductor integrated circuits and the like.

A contact exposure apparatus that uses evanescent light is proposed asone such exposure apparatus in, for example, U.S. Pat. No. 6,171,730.The invention described in U.S. Pat. No. 6,171,730 is excellent, andmakes a significant contribution to the areas of photolithography andsemiconductor manufacturing technology. The exposure apparatus describedin U.S. Pat. No. 6,171,730 is shown in FIG. 14.

In the apparatus shown in FIG. 14, a resist film 107 is formed on thesurface of a substrate (wafer) 106 so as to prepare an object to beexposed. The substrate is attached on stage 108 and the stage 108 isdriven to align the substrate 106 relative to a photomask 101. The stage108 is driven in a direction normal to the mask surface to bring thephotomask 101 into intimate contact with the resist 107 on the substrate106, and the resist 107 is exposed to evanescent light generated in thevicinity of fine apertures on the front of the photomask 101, by the useof exposure light 110 emitted from an exposure light source 109.

With respect to the alignment between the above-described photomask andthe substrate in such a contact exposure apparatus, only the alignmentof the substrate (wafer) relative to the photomask has been previouslyperformed in the two-dimensional direction on the mask surface, that is,only horizontal alignment is performed, and performing alignment throughthe use of a microscope observation is conventional.

However, in known contact exposure apparatuses, no device for measuringand controlling the distance between a mask and a wafer is provided, andonly horizontal alignment is performed to align the mask with the wafer,as described above. Consequently, the measurement and the control of thedistance between a mask and a wafer required in the case of, forexample, exposure to the evanescent light by the use of an intimatelycontacted mask cannot be performed.

With respect to the horizontal alignment through the use of a microscopeobservation in a known contact exposure apparatus, the accuracy of thealignment may be on the order of 1 μm, and may not be comparable to theaccuracy (100 nm or better) required of an evanescent-light exposureapparatus, for example.

If the construction of the device for measuring and controlling thedistance between a mask and a wafer is attempted by the use of, forexample, known distance-measuring technology, e.g., laser telemetry, theconfiguration of the apparatus becomes complicated significantly.

SUMMARY OF THE INVENTION

Accordingly, it is an object of the present invention to provide aposition sensor capable of highly accurate detection of a position inhorizontal and vertical directions without the need for a complicatedmechanism, and to provide an alignment apparatus including the positionsensor.

A position sensor of the present invention includes an excitation lightsource and an interface structure comprising a surface plasmon waveguideformed of a dielectric between negative dielectrics, and has aconfiguration in which the plasmon intensity with respect to amicrostructure on a surface including the interface structure or in thevicinity thereof is detected by the interface structure, and thepositional relationship between the interface structure and themicrostructure is thereby detected.

In the position sensor of the present invention, desirably, interfacesof the interface structure are parallel to each other, and normals tothe interface structure are present in the same plane.

The position sensor of the present invention may have a plurality ofinterface structures, and may have a configuration in which theabove-described interface structures are arranged close to each other.

The position sensor of the present invention may have a configuration inwhich the plurality of interface structures are arranged in the shape ofa straight line, a cross, a ring, or an array.

A method for detecting a position of a substrate in the presentinvention includes the step of preparing an interface structure whichfunctions as a waveguide of surface plasmon and in which a dielectric issandwiched between negative dielectrics and the step of detecting thepositional relationship between the above-described interface structureand an object to be detected by passing excitation light through theabove-described interface structure to generate localized plasmon, anddetecting fluctuations of the localized plasmon due to the presence ofthe object to be detected.

An alignment apparatus of the present invention includes theabove-described position sensor, and a substrate with a microstructureon a surface therein positioned below said interface structure, whereinplasmon intensity with respect to the microstructure on the surface isdetected by the interface structure, and alignment therebetween isperformed.

In the alignment apparatus of the present invention, the above-describedinterface structure may be provided in the above-described mask.

In the alignment apparatus of the present invention, the above-describedinterface structure may be provided substantially penetrating throughthe substrate of the above-described mask including the interfacestructure.

In the alignment apparatus of the present invention, a light-shieldinglayer of the above-described mask may be formed from a negativedielectric.

In the alignment apparatus of the present invention, the above-describedmicrostructure may be made of a metal.

The alignment apparatus of the present invention may have aconfiguration in which the above-described microstructure is provided ona substrate to be exposed, while the microstructure may be provided as aconcave portion or a convex portion.

The alignment apparatus of the present invention may have aconfiguration in which the height of the above-described microstructurefrom the surface of the above-described substrate to be exposed islarger than or nearly equal to the thickness of a photosensitivematerial film provided on the substrate to be exposed.

A method for alignment provided by the present invention includes thesteps of preparing an interface structure comprising a surface plasmonwaveguide formed of a dielectric sandwiched between negativedielectrics, the step of detecting the positional relationship betweenthe above-described interface structure and an object on a substrate tobe detected by passing excitation light through the above-describedinterface structure to generate localized plasmon at an outlet of theinterface structure and detecting fluctuations of the localized plasmondue to the presence of the object to be detected, and the step ofcontrolling the positions of the above-described interface structure andthe above-described object to be detected based on the above-describedpositional relationship.

The present invention can provide a position sensor capable of detectinga position in horizontal and vertical directions with a high accuracy,on the order of 100 nm or better, without the need for a complicatedmechanism, as well as an alignment apparatus including the positionsensor.

According to the present invention, detection of a position as well asalignment can be performed with a high accuracy, on the order of 100 nmor better.

Further objects, features and advantages of the present invention willbecome apparent from the following description of the preferredembodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram for explaining a principle of the present inventionwith reference to a plasmon waveguide structure in which a thin filmdielectric is sandwiched between negative dielectrics in an embodimentof the present invention.

FIG. 2 is a diagram for explaining the detection of the reflectionintensity of plasmon in an embodiment of the present invention.

FIG. 3 is a schematic diagram showing the relationship between theamount of horizontal deviation and the reflection intensity of plasmonin an embodiment of the present invention.

FIG. 4 is a schematic diagram showing the relationship between thedistance from a waveguide to a marker in a vertical direction and thereflection intensity of plasmon in an embodiment of the presentinvention.

FIG. 5 is a diagram showing examples of the shape of a plasmon waveguidestructure in an embodiment of the present invention.

FIG. 6 is a diagram showing examples of a marker structure in anembodiment of the present invention.

FIGS. 7A to 7C are diagrams showing examples of the arrangement of aplurality of plasmon waveguide structures in an embodiment of thepresent invention.

FIGS. 8A to 8F are diagrams showing a part of the steps in an Exampleaccording to the present invention.

FIGS. 9A and 9B are diagrams showing a part of the steps in an Exampleaccording to the present invention.

FIG. 10 is a diagram showing a part of the steps in an Example accordingto the present invention.

FIG. 11 is a diagram showing a part of the steps in an Example accordingto the present invention.

FIG. 12 is a diagram showing a part of the steps in an Example accordingto the present invention.

FIG. 13 is a diagram showing a part of the steps in an Example accordingto the present invention.

FIG. 14 is a diagram showing the configuration of an example of a knownevanescent-light exposure apparatus.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the position sensor of the present invention, an interface structurebetween negative dielectrics and a dielectric is configured, asdescribed above. Specifically, a plasmon waveguide corresponding to asmall probe is configured, and the plasmon intensity based on astructural element, e.g., a marker, in the vicinity of the waveguideoutlet is detected through the use of the plasmon waveguide. As aresult, the distance between the plasmon waveguide and the marker in ahorizontal direction or the distance between the plasmon waveguide andthe marker in a vertical direction is controlled. In the presentinvention, negative dielectric means a member whose dielectricpermittivity is negative.

Such a plasmon waveguide will be specifically described below.

In a structure in which a thin film dielectric is sandwiched betweennegative dielectrics shown in FIG. 1, a coupling mode (hereafterreferred to as Fano mode) of surface plasmon at both interfaces ispresent, and a propagation mode is included therein, while no matter howsmall the film thickness of the dielectric thin film is, the propagationmode has no cutoff. The beam diameter of this mode can be reduced to thesize smaller than or equal to the wavelength of the light by reducingthe film thickness of the dielectric thin film to a size smaller than orequal to the wavelength of the light.

FIG. 1 is a schematic diagram illustrating a Fano mode used for, e.g.,alignment.

In FIG. 1, when the surface plasmon is transmitted through thedielectric thin film and reaches the waveguide outlet, localized plasmonis formed in the vicinity of the outlet. This localized plasmon expandsin a region having a size nearly equal to the diameter of the waveguideoutlet. If another material is present in the region in which thelocalized plasmon is generated, the localized plasmon is fluctuated bythis material.

If a material, e.g., a metal piece, is present in the vicinity of thewaveguide outlet, a part of the localized plasmon is converted topropagation light and scattered, and a part of the localized plasmon isreflected so as to return through the waveguide.

Since the reflectance of this plasmon varies depending on the dielectricconstant distribution in the vicinity of the waveguide outlet,reflectances are different in the case where a photoresist is present inthe vicinity of the waveguide outlet, the case where a metal is present,and the case where a semiconductor or the like is present. Consequently,when the dielectric constant is changed because, for example, anothermaterial enters a very small region of expanded localized plasmon, thelocalized plasmon is influenced and, thereby, the reflectivity of thesurface plasmon in the vicinity of the waveguide outlet is alsoinfluenced.

The basic principle of the present invention is to detect whether anymaterial is present in the vicinity of the waveguide outlet, and morespecifically, whether any structure, e.g., a marker, is present, with asmall probe referred to as “localized plasmon” through the use of theabove-described principle.

In order to provide a noticeable change in reflectance, it is preferablefor the region in which the dielectric constant distribution is changedto be in close proximity to the waveguide outlet. It is preferable thatthe distance Δ between the waveguide outlet and the material is about100 nm or less.

In an alignment method of the present embodiment, for example, theabove-described plasmon waveguide is prepared on a photomask, and amaterial that functions to scatter or reflect the localized plasmon isprepared as a marker on a substrate. For example, the configurationshown in FIG. 2 is provided, and the reflection intensity of the plasmonis detected. FIG. 3 and FIG. 4 are schematic diagrams showing the changein the reflection intensity of plasmon in relation to the positionalrelationship between the waveguide and the marker.

When the marker is present in the vicinity of the surface plasmonwaveguide outlet, the intensity of the reflected plasmon is large. Onthe other hand, when the marker is not present in the vicinity of theplasmon waveguide outlet (either when there is a deviation in thehorizontal position or when the distance between the mask and thesubstrate is large), the reflection intensity of the plasmon is small.Therefore, by monitoring the reflection intensity of the plasmon, thealignment between the plasmon waveguide and the marker in a horizontaldirection and the distance between the mask and the marker in a verticaldirection can be determined.

In order to excite the plasmon, excitation light may be condensed in thevicinity of the plasmon waveguide inlet and applied. However, thepolarization direction of the excitation light must be controlled inaccordance with the shape of the plasmon waveguide. Since the plasmon isexcited basically by TM wave, when the waveguide is in the shape of, forexample, a slit, the excitation is preferably performed by the lightpolarized in the direction perpendicular to the slit. The reflectionintensity of the plasmon may be measured by, for example, scanning thevicinity of the plasmon waveguide inlet with a metal microprobe or thelike. Alternatively, the change in intensity of the scattered light,which is generated from the plasmon and returns to the plasmon waveguideinlet, may be measured.

With respect to the shape of the waveguide layer, it is particularlydesirable that interfaces are parallel to each other, that is, the widthof the waveguide layer is constant. This is because the mode of plasmonis not stable if the parallelism of the interfaces is low, and thetransmission of the plasmon is hindered if the interface is not smooth.

It is desirable that the size and the shape of the marker at this timeare approximately equal to the size and the shape of the outlet of thedielectric layer of the waveguide. If the size of the marker is toolarge relative to the area of the waveguide outlet, the alignmentaccuracy is reduced. If the size of the marker is too small, thedetection of the change in reflectance of the plasmon becomes difficult.

The shape of the waveguide outlet and the shape of the marker are notnecessarily the shape of a dot. The shape of a cross, the shape of aletter L, and the like may be adopted, as shown in FIG. 5. The shape ofa ring may also be adopted.

The ring may be in the shape of concentric circles. However, it isconsistently desirable that the shape of the marker is substantiallyequal to the shape of the dielectric layer of the plasmon waveguide. Inthis case as well, it is desirable that the shape of the waveguideoutlet and the shape of the marker are substantially the same.

As shown in FIG. 6, it is desirable for the shape of the marker to havea convex structure because the distance between the waveguide outlet andthe marker can be decreased during the alignment. Since a photoresist isgenerally applied on the substrate, the marker having a convex structureis prepared. In addition, the thickness of the photoresist layer at themarker top is very thin and, therefore, the substantial change indielectric constant and reflectance in the vicinity of the marker topcan be readily increased. However, the substrate to be exposed may notbe processed into the convex structure by the use of a batch process orother means, but some metal piece may be attached to the flat surface ofthe substrate to be exposed. Conversely, the substrate may be allowed tohave a concave structure, and a change in reflectance and a change indielectric constant may be effectively generated relative to thesurrounding thereof. The concave structure can readily be prepareddirectly at the portion required to have the concave structure by theuse of a focused ion beam (FIB) processing apparatus or other apparatuscapable of performing fine processing.

The sizes of the marker and the waveguide outlet are allowed to becomelarge to some extent (in the order of several micrometers) and, thereby,a shift from rough alignment to fine alignment becomes easy. The methodfor alignment of the present invention may be used just as finealignment, and a rough alignment mechanism may be prepared separately.

A plurality of plasmon waveguide structures and a plurality of markersmay be disposed on a mask and a substrate. For example, the arrangementof them may be in the shape of a straight line or an array, as shown inFIGS. 7A to 7B, a two-dimensional array, as shown in FIG. 7C, or be inthe shape of a cross or a ring.

EXAMPLE

With respect to this Example of the present invention, a configurationin which a plasmon waveguide structure of the present invention isincorporated in a photomask of an evanescent-light exposure apparatus,as shown in FIG. 14, will be described. In the present Example, theplasmon waveguide structure is prepared on the substrate of a photomaskof the evanescent-light exposure apparatus according to the followingsteps.

A Si substrate 1 with surface orientation 100 is prepared (FIG. 8A).

Mask matrices 2 made of Si₃N₄ were formed into films of 500 nm with alow pressure chemical vapor deposition apparatus (LPCVD apparatus) onboth surfaces of this substrate (FIG. 8B).

A back etch hole 3 was patterned with CF₄ on the back of the substrate 1(FIG. 8C).

The substrate 1 was subjected to crystal axis anisotropic etching, sothat a mask thin film portion 4 made of the mask matrix was formed (FIG.8D).

A through hole 5 and a through hole 6, each having a diameter of about100 nm, were prepared at locations close to the end of this mask thinfilm portion 4 (points A and B located at a distance of 2 mm from thecenter of the mask thin film portion) with an FIB processing apparatus(FIG. 8E). The device for preparing the through holes is not limited tothe FIB processing apparatus.

A Cr film of 40 nm serving as a metal layer 7 was formed with a metalCVD apparatus. The metal to be formed into a film with the metal CVDapparatus is not limited to Cr. Metals suitable for readily transmittingthe Fano mode are particularly preferable.

A Si₃N₄ film serving as a dielectric layer 8 was formed with the LPCVDapparatus, so that the through holes were filled in (FIG. 8F).

The dielectric layers 8 on both surfaces of the substrate 1 were etchedwith a reactive ion etching (RIE) apparatus and, thereafter, the metallayer 7 on the back of the substrate 1 was etched with a metal RIEapparatus. As a result, the metal layer 7 and the dielectric layer 8remained in the through holes and on the front side. A resist layer 9was applied to the front of the substrate 1, and a pattern 10 and apattern 11 to provide windows for rough alignment were prepared (FIG.9A).

The metal layer 7 was removed from the portions corresponding to thepattern 10 and the pattern 11 by dry etching. The pattern 10 and thepattern 11 are each 1 mm square, and a marker 12 and a marker 13 foralignment were provided therein. The marker 12 and the marker 13 areeach 10 μm, and are in the shape of a cross, as shown in FIG. 13. Theresist layer 9 was removed, so that plasmon waveguide structures 22 and23 were prepared on the substrate 1 (FIG. 9B).

A mask pattern 14 was prepared on a desired place of the metal layer 7of the substrate 1 (in the present Example, on the surface opposite tothe back etch hole of the back), so that a photomask 100 was completed(FIG. 10).

A substrate 21 provided with a marker 15, a marker 16, a marker 19, anda marker 20 for alignment was prepared beforehand as a substrate to beexposed by the use of an apparatus capable of performing electron beam(EB) processing, FIB processing, or other fine processing (FIG. 11).

This substrate 21 provided with the markers 15, 16, 19, and 20 foralignment was brought close to the photomask 100 provided with theplasmon waveguide structures 22 and 23, white light was applied to theplasmon waveguide structures 22 and 23 to excite plasmon, roughalignment was performed as described below and, thereafter, finealignment was performed.

As the distance between the photomask 100 and the substrate 21 changes,a change in the reflection intensity of plasmon is measured. A positionat which the reflection intensity of plasmon sharply changes dependingon the distance between the photomask 100 and the substrate 21 isdetermined, and the alignment between the photomask 100 and thesubstrate 21 in a horizontal direction is performed.

The waveguide structure is brought above the position at which themarker is assumed to be present, the distance between the photomask 100and the substrate 21 is decreased, and further alignment in a horizontaldirection is performed. After the alignment in a horizontal direction iscompleted, distance control in a vertical direction is performed. Thereflection intensity of plasmon is increased as the distance between thephotomask 100 and the substrate 21 is decreased. When the photomask 100and the substrate 21 is substantially brought into contact with eachother, the increase in the intensity comes to a halt. Therefore, thedistance between the photomask 100 and the substrate 21 is maintained tobe such a distance at which the reflection intensity of plasmon isslightly smaller than the maximum.

As described above, by using the photomask 100 and the substrate 21, thealignment in a horizontal direction (horizontal direction relative tothe substrate 21) can be performed with high accuracy of about 100 nm orbetter through a simple alignment structure. The distance control in avertical direction (direction perpendicular to the substrate 21) canalso be performed with high accuracy of about 100 nm or better.

In the present Example, Si₃N₄ is embedded as a dielectric. However, thedielectric is not limited to this material. Air may be used. In thepresent Example, the waveguide structure penetrates through thephotomask. However, the structure may not penetrate through thephotomask. In the present Example, the marker is prepared to have theshape shown in FIG. 12. However, the shape is not limited to the shapeshown in FIG. 12. Likewise, the size is not limited to the sizesexplained in the present embodiment and Example.

The markers 15, 16, 19, and 20 of the substrate 21 may not be providedwith the metal layer 17 nor metal layer 18 on the tops thereof.

The marker may not be the convex portion. Conversely, the marker may bea concave portion. The concave structure may be formed directly on thesubstrate by the use of an FIB processing apparatus or other apparatusescapable of performing fine processing. The concave structure can beprepared directly on the substrate without going through the batchprocess or the like and, therefore, can be prepared readily.

While the present invention has been described with reference to whatare presently considered to be the preferred embodiments, it is to beunderstood that the invention is not limited to the disclosedembodiments. On the contrary, the invention is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. A position sensor comprising: an excitation light source; aninterface structure comprising a surface plasmon waveguide formed of adielectric, said interface structure sandwiched between negativedielectrics and adapted to be positioned over a substrate.
 2. Theposition sensor according to claim 1, wherein interfaces of saidinterface structure are in parallel.
 3. The position sensor according toclaim 1, wherein normals to the interface structure are present in thesame plane.
 4. The position sensor according to claim 1, furthercomprising a plurality of interface structures.
 5. The position sensoraccording to claim 4, wherein the plurality of interface structures areeach shaped as one of a straight line, a cross, a ring, and an array. 6.A method for detecting a position of a substrate, comprising the stepsof: preparing an interface structure which functions as a waveguide ofsurface plasmon and in which a dielectric is sandwiched between negativedielectrics; and detecting the positional relationship between theinterface structure and an object on the substrate to be detected bypassing excitation light through the interface structure to generatelocalized plasmon at an outlet of the interface structure, and detectingfluctuations of the localized plasmon due to the presence of the objectto be detected.
 7. An alignment apparatus comprising: an excitationlight source; an interface structure comprising a surface plasmonwaveguide formed of a dielectric, said interface structure sandwichedbetween negative dielectrics; and a substrate with a microstructure on asurface therein positioned below said interface structure, whereinplasmon intensity with respect to the microstructure on the surface isdetected by the interface structure, and the positional relationshipbetween the interface structure and the microstructure is therebydetected.
 8. The alignment apparatus according to claim 7, wherein theinterface structure is provided in a mask.
 9. The alignment apparatusaccording to claim 8, wherein the interface structure penetrates throughthe substrate of the mask comprising the interface structure.
 10. Thealignment apparatus according to claim 8, wherein a light-shieldinglayer of the mask comprises a negative dielectric.
 11. The alignmentapparatus according to claim 7, wherein the microstructure comprises ametal.
 12. The alignment apparatus according to claim 7, wherein themicrostructure is provided as a concave portion on the substrate to beexposed.
 13. The alignment apparatus according to claim 12, wherein themicrostructure is provided as a concave portion on the substrate to beexposed.
 14. The alignment apparatus according to claim 12, wherein themicrostructure is provided as a convex portion on the substrate to beexposed.
 15. The alignment apparatus according to claim 7, wherein theheight of the microstructure from the surface of the substrate to beexposed is at least as great as a thickness of a photosensitive materialfilm provided on the substrate to be exposed.
 16. A method foralignment, comprising the steps of: preparing an interface structurecomprising a surface plasmon waveguide formed of a dielectric sandwichedbetween negative dielectrics; detecting the positional relationshipbetween the interface structure and an object on a substrate to bedetected by passing excitation light through the interface structure togenerate localized plasmon at an outlet of the interface structure anddetecting fluctuations of the localized plasmon due to the presence ofthe object to be detected; and controlling the positions of theinterface structure and the object to be detected based on the detectedpositional relationship.